Apparatus for degassing molten metal



March 21, 1967 Filed April 23, 1962 R. J. TAYLOR APPARATUS FOR DEGASSING MOLTEN METAL 5 Sheets-Sheet 1 INVENTOR.

Robert J 75 502" March .21, 1967 R. J. TAYLOR APPARATUS FOR DEGASSING MOLTEN METAL s sheets-sheet 2 7 Filed April 23. 1962 INVENTOR.

March 21, 1967 R. J. TAYLOR APPARATUS FOR DEGASSING MOLTEN METAL 3 Sheets-Sheet 5 Filed April 25, 1962 United States Patent 3,310,296 APPARATUS FOR DEGASSING -MOLTEN METAL Robert J. Taylor, McKees Rocks, Pa., assiguor to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Apr. 23, 1962, Ser. No. 189,397 14 Claims. (Cl. 266-34) This invention relates to apparatus for the vacuum degassing of molten metals and more particularly to stroke control means for a vacuum degassing apparatus having a relatively movable vacuum vessel and molten metal container.

The type of vacuum degassing apparatus in which the instant invention is incorporated, is one wherein a vacuum chamber is disposed above a ladle of molten metal and the two are arranged for relative movement toward and away from each other. A nozzle extends downwardly from the lower end of the vacuum chamber so that upon relative movement of the chamber and the ladle toward each other, the reduced pressure within the chamber draws molten metal through the nozzle and into the chamber for vacuum treatment. Upon relative movement of the chamber and ladle away from each other, molten metal discharges through the nozzle to intermix with the remaining metal within the ladle. If desired, a new portion of the melt may be drawn into the chamber by again relatively moving the vessel and ladle toward each other. This process is repeated until the desired degree of total degasification has been achieved.

It can be seen that in order to maintain the vacuum within the chamber during relative movement of the ladle and chamber away from each other, it is necessary for the lower end of the nozzle to remain immersed below the level of the molten metal within the ladle. In addition, when the ladle and vessel are moving toward each other, it is obviously necessary to arrest such movement short of engagement.

It is an object of the instant invention to provide stroke control means for the relatively movable containers of a vacuum degassing apparatus.

It is another object of the instant invention to provide cyclical vacuum apparatus having a relatively movable vacuum vessel and container with tracking means for sensing the relative position of the vessel and container and control means for arresting relative movement when preselected limits in either direction is reached. Another object of the invention is to provide such control means with means for adjusting the limits of relative movement.

A further object of the invention is 'to provide the relatively movable portions of a cyclic vacuum degassing apparatus with control means having first and second adjustable means for establishing the travel limits of said portions and first and second motive means for the adjustable means wherein control means is operative to individually de-actuate the motive means when its associated adjustable means achieves a position corresponding to the relative positions of said portions.

Yet another object of the invention is to provide vacuum apparatus having a relatively movable vessel and container with tracking means for producing an electrical signal reflective of the relative positions of the vessel and container and control means having means for producing first and second reference signals, and signal comparison means for arresting relative movement in one direction or the other when said electrical signal bears a predetermined relation to one or the other of said reference signals.

These and other objects and advantages of the instant invention will become more apparent from a detailed Patented Mar. 21, 1967 "ice description thereof taken with the accompanying drawings in which:

FIG. 1 schematically illustrates the vacuum degassing apparatus with which the instant invention is used;

FIG. 2 is a circuit diagram illustrating a portion of the stroke control means according to the instant invention;

FIG. 3 schematically illustrates another portion of the stroke control means of the instant invention.

Referring now to the drawings in greater detail, FIG. 1 schematically illustrates vacuum degassing apparatus in which the instant invention is usable. This apparatus is shown to include a vessel 10, a ladle 11 containing molten metal 12 and lifting mechanism 14 for supporting the vacuum chamber and for moving it vertically relative to the ladle 11. The degassing vessel 10 includes a steel shell 15 which encloses an inner refractory lining 16. A layer of heat insulating material 18 is disposed between the metallic shell 15 and the refractory lining 16, to minimize heat radiation losses from the vessel 10. The steel shell 15 provides a support for and hermetically seals the chamber 23 defined by the relatively porous refractory lining 16.

A nozzle 20 is affixed to the lower end of the vessel 10 and has a cylindrical bore 22 that communicates with the chamber 23 defined by the refractory lining 16. The lower end of the nozzle 20, which extends below the surface of the melt 12, during a degassing operation is also provided with refractory material at its outer surface to prevent contact between the metallic shell 15 and the adjacent an aperture 28 and the roof 29 of refractory lining 16. A car 30, movably mounted on rails 32 below vessel 10 is provided to support and position the ladle 11. The lifting mechanism 14 includes a platform 34 upon which the vessel 10 is affixed and a plurality of coordinated hydraulic rams 36, each consisting of a piston 37 and a cylinder 38, for moving the platform 34 and the vessel 10 vertically.

Operation of the vacuum degassing apparatus will first be discussed so that the functions of the stroke control unit according to the instant invention can be more fully appreciated. After the ladle 11 of molten metal 12 has been positioned below the vessel 10, the latter is lowered until the nozzle 20 extends a predetermined distance below the surface of the melt 12 as indicated by dotted lines in FIG. 1. Evacuating apparatus 24 is then energized to produce a partial vacuum within the chamber 23. As a result of the difference in pressure between the interior of chamber 23 and that atmospheric pressure acting on the surface of the melt 12, a portion of said melt, identified by the reference numeral 12' to distinguish it from the main body of melt 12, is forced upward through nozzle 20 and into chamber 23 where gases dissolved therein are drawn off by the operation of the partial vacuum. After this portion 12' of the melt 12 has been degassed for a predetermined length of time, the vessel 10 is raised to its position shown by full lines, thereby causing the melt 12 to discharge into the ladle 11 to produce a vigorous stirring within the remainder of the melt 12. The lower end of the nozzle 20, however, remains below the surface of the melt 12 to maintain the partial vacuum within the chamber 23. This process may then be repeated, by successively lowering and raising vessel 10 until the desired degree of total degasification has been achieved.

The height to which the molten metal 12' will rise above the surface of the metal 12 in the ladle 11, when the vessel 10 is in its dotted position in FIG. -1, is the barometric height of the metal, which for steel is approximately 4.7 feet.

While the means for driving the hydraulic rams 36 may be of any conventional well-known type, the illustrated arrangement consists of a pump 40 which is continuously driven by a motor 42. The pump 40 is connected by conduits 44 and 45 to the pressure side of the piston 38. A valve 46 is disposed between the conduits 44 and 45 and is controlled by a solenoid 47. When the solenoid 47 is de-energized the valve 46 is in the position shown in FIG. 1 wherein it connects the conduit 44 to a sump 49 through the conduit 50. When the solenoid 47 is energized the valve 46 is rotated 90 degrees counterclockwise so that the output of the pump 40 is connected to the piston 37 through the conduit 45, whereby the platform 34 and the vessel will be raised vertically.

A second valve 54 controlled by a second solenoid 55 is disposed in a conduit 56 which connects the pressure side of piston 37 with the sump 49. When the solenoid 55 is de-energized the valve 54 is in its position shown in FIG. 1 wherein flow from the piston 37 to the sump 49 is prevented. When the solenoid 55 is energized, on the other hand, the valve 54 will be rotated 90 degrees to connect the piston 37 to the sump 49 so that the piston 37 and the vessel 10 will be allowed to move vertically downward. It will be appreciated by those skilled in the art that the rate of ascent and descent of the vessel 10 will be controlled by the rate of which fluid is delivered through the conduit 52 and vented through the conduit 56 and that these rates may be controlled by means well known in the art.

The solenoids 47 and 55 are controlled by the control circuit 60 shown in FIG. 2 which, in turn, is actuated by the position tracking means 62 provided for sensing the position of the vessel 10 relative to the ladle 11 and for providing an appropriate signal to control circuit 60 when cessation of a raising or lowering operation is indicated. As will be discussed in greater detail hereinafter, the control circuit 60 includes a lower limit portion L having a relay 85 which is de-energized when the platform 34 is above its lower limit and which becomes energized when the lower limit is reached. In addition, the control circuit 60 includes an upper limit portion U having a relay 86 which is de-energized when the platform 34 is below its upper limit and which becomes energized when the upper limit is reached.

Referring again to FIG. 1, the solenoids 47 and 55 are shown to be in circuit between the conductors 128 and 129 of any suitable supply source. Also connectable between the conductors 128 and 129 by means of a selector switch 130 is a raising automatic relay 132 and a lowering automatic relay 134. It can be seen that when the contact 135 of selector switch 130 is closed, raising relay 132 will be energized to close contacts 132A between the solenoid 47 and conductor 128 and when contact 136 is in the closed position relay 134 will be energized to close contacts 134A between lowering solenoid 55 and conductor 128.

Also connected between solenoid 47 and conductor 128 are the normally closed contacts 86A of relay 86 while the normally closed contacts 85A of relay 85 are connected between solenoid 55 and conductor 128.

When a degassing operation is to be commenced, the platform 34 will be in an elevated position and a, ladle 11 will be positioned therebeneath. When in this position, platform 34 will be above its upper limit so that relay 86 of FIG. 2 will be energized and normally closed contacts 86A will be opened to maintain solenoid 47 de-energized. Contacts 136 will be manually placed in closed position to energize relay 134 which closes contacts 134A to complete the circuit through the lowering solenoid 55. This opens the valve 54 to connect the pressure side of cylinder 37 to the sump 56 and the platform 34 and vessel 10 begins lowering toward the ladle 11. As the lower end of nozzle 20 becomes immersed in the melt 12, the upper reference point of the platform 34 will be reached and relay 86 will become de-energized to close the contacts 86A. As the platform 34 continues descending it will reach the lower reference point to energize the relay thereby opening the contacts 85A and de-energizing the solenoid 55. Upon this event the valve 54 closes to disconnect the pressure side of piston 37 from the sump 49 and prevent further downward movement of the vessel 10.

When the lower set point is reached the vacuum apparatus 24 is actuated to produce a vacuum within the chamber 23 and thereby draw molten metal 12' into the interior of vessel 10.

After such degasification has continued for a predetermined length of time, selector switch will again be operated to close the contacts and open the contacts 136 to thereby energize the relay 132 and close the contacts 132A. This energizes solenoid 47 which initiates a raising operation. As the vessel 10 rises, the molten metal 12' will discharge into the ladle 11 to intermix with the remainder of the metal 12. However, before the lower end of the nozzle 20 leaves the body of metal 12, which would destroy the vacuum within the chamber 23, relay 86 is energized to open contacts 86A and de-energize the solenoid 47. This stops the vessel 10 in its upper reference point shown by full lines in FIG. 1.

The tracking means 62 is shown in FIGS. 1 and 2 to include a rack 64 rigidly affixed to the platform 34 and movable vertically therewith. The rack 64 meshingly engages a pinion 65 which is mechanically coupled to drive the wiper 67 of a potentiometer 68. It can be seen that downward movement of the vessel 10 will rotate the pinion 65 and the Wiper 67 counterclockwise to increase the potential at the wiper terminal 70. Conversely, upward movement of the platform 35 will rotate the pinion 65 and wiper 66 clockwise to decrease the potential at wiper terminal 70. Thus, it will be appreciated that the potential on wiper terminal 70 will be a function of the position of platform 34 relative to the ladle 11.

As seen in FIGS. 1 and 2, the potentiometer 68 is connected in series with a pair of ganged adjustable resistors 72 and the series combination is connected across the positive and negative terminals 73 and 74 respectively, of a constant voltage source. It can be seen that the potential on wiper terminal 78 will also be a function of the resistance of resistors 72 so that their adjustment determines the total span of travel of the platform 34 during the cyclic raising and lowering operations of a degassing operation. This will normally be adjusted to be something less than the barometric height of the metal being treated.

Referring now specifically to FIG. 2, the control circuit 60 is shown to include an upper limit portion U and a lower limit portion L. Each of these portions contain like components and such corresponding components in each portion will be given the same reference numerals, distinguished by means of a prime in the case of the upper limit portion U.

The lower limit portion L includes a first transistor T1 of the PNP type, whose collector is connected to the base of the second PNP transistor T2. The emitter-collector circuit of transistor T2 is connected in parallel with a relay winding 85 so that when T2 emitter-collector current flows the relay winding 85 is short circuited, and hence effectively de-energized. In a similar manner, the upper limit portion U is provided with a PNP type transistor T3 whose emitter is connected to the base of a second PNP type transistor T4. In the upper limit portion U, however, relay winding 86 is in series with the collector of transistor T4 so that it will be energized when T4 is conductive.

Each of the portions L and U are also shown to include an adjustable potentiometer P1 and P2, respectively.

The reference points of the portions L and U of the circuit 62, that is, the upper and lower positions of the platform 34 at which either the L or the U portion will be actuated, is determined by the positions of the adjustable taps or wipers 87 and 87' of the potentiometers P1 and P2. Tap 87 is positioned by a motor 120 and a clutch 122 which is actuated by a solenoid 123. Similarly, the tap 87' is adjustable by means of a motor 120, a clutch 122 and the solenoid 123. The means for energizing the motors 120 and 120' and the solenoids 123 and 123' will be discussed in greater detail hereinbelow. It will be suflicient at this point to state that the positions of wiper 87 will determine the lower limit of platform 34 and the position of wiper 87' will determine its upper limit. It will be understood that the terms upper limit and lower limit refer to the travel limits during the cyclic drawing in and discharging of molten metal from the vessel 10, and that at the termination of this cyclic operation the vessel is movable outside of these limits by means to be described.

Operating energy is supplied to the circuit 60 by a transformer 88 having one secondary winding 90 connected to the lower limit portion L and another secondary winding 91 connected to the upper limit portion U. A coupling capacitor C1 and a diode D1 connect the secondary winding 90 to the portion L so that uni-directional energy is provided at the power input terminals 94 and 95 of said portion. A conductor 97 connects the positive power supply terminal 95 to the emitter of transistor T1 through conductor 98 and to the emitter of T2 through diode 100. The positive terminal 102 of potentiometer P1 is connected to conductor 98 through a diode 104 while the negative terminal 105 of P1 is connected to the negative supply terminal 94 through conductor 106,

resistor 107, conductor 109, resistor 111 and conductor 112. Resistor 113 connects the negative terminal 94 to the collector of T2 and the relay 85.

A Zener diode 92, which is a circuit element characterized by having a substantially uniform breakdown voltage in a reverse direction regardless of the current flowing through it, is connected between conductors 97 and 109 to provide a relatively constant potential across the circuit consisting of the potentiometer P1 and the resistor 107.

The portions L and U of the control circuit 60 are each coupled to receive current signals proportional to the potential on the tap 70 of potentiometer 68, by means of resistors R1 and R2, respectively, which, along with a current limiting resistor R3, are connected in shunt across the positive voltage source terminal 73 and the Wiper 70.

With reference to the lower portion L, it can be seen that the potentiometer P1 between tap 87 and terminal 102 and the resistors R1 and 119 are connected between the emitter and base of transistor T1. Resistor R1 is also in circuit between the positive supply terminal 73 and the wiper terminal 70 so that it will receive a current proportional to the position of wiper 67. Also, potentiometer P1 is connected to a relatively constant voltage source consisting of Zener diode 92, so that the current flowing through it will be relatively constant. It can be seen, therefore, that the potential difference between the emitter and base of transistor T1 will be a function of both the position of wiper 67 of potentiometer 68 and of the wiper 87 of potentiometer P1. In a similar manner, the potential difference between the emitter and base of transistor T3 will be a function of the position of wiper 67 and the position of wiper 87' of potentiometer P2.

For purposes of illustration, assume that each of the wipers 87 and 87' have been set to obtain the desired upper and lower limits. That is, an upper limit shown by full lines in FIG. 1 wherein the end of the nozzle 20 remains below the level of the metal 12, and a lower limit shown by dotted lines wherein the lower end of the vessel 10 is above the rim of the ladle 11. When platform 34 is in mid-span, that is, between its upper .6 and lower limits, the resistances of resistors R1, 119 and potentiometer P1 between the terminal 102 and the tap 87 and potentiometer 68 between terminal 73 and wiper 67 will be such that the base of transistor T1 will be positive relative to its emitter. As a result, no collector current will flow from transistor T1 to a biasing resistor 125, connected at one end to the emitter of transistor T1 and the base of transistor T2 and at its other end to conductor 109. Because no current flows in resistor 125, the base of transistor T2 will be at the potential of the negative power supply terminal 94 plus the drop in resistor 111 and hence negative relative to its emitter whose potential is equal to that of the positive power supply terminal minus the drop in diode 100. As a result, emitter-collector current will flow in transistor T2 thereby short circuiting the relay winding 85 so that the latter is de-energized.

Similarly, when the platform 34 is in mid-span, the resistances of resistors 119' and R2 and of potentiometer P2 between terminal 102' and tap 87' and the position of wiper terminal 67 will be such that the potential on the base of transistor T3 is less than its emitter potential so that this transistor is conductive. As a result, current flows through resistor to hold the base potential of transistor T 4 at a positive value relative to its emitter. Transistor T4 will therefore be non-conductive so'that no collector current will flow to relay winding 86 which will be de-energized.

Assume now that the platform 34 is moving downwardly to its phantom position in FIG. 2, so that the wiper 67 of potentiometer 68 will be moved counterclockwise from its full position toward its dotted position thereby decreasing the potential difference between terminal 73 and the wiper terminal 70. This will proportionately reduce the current flowing in resistor R1 and thereby lower the potential of the base of transistor T1 relative to its emitter. When the platform 34 reaches its preselected lower limit, determined by the position of wiper 87, the base of transistor T1 will become sufficiently negative relative to its emitter to cause collector current to begin flowing in transistor T1. This collector current flowing through resistor 125 will raise the potential of the base of transistor T2 above its emitter potential so that the latter will become non-conductive. As a result, current is no longer by-passed around relay 85 and it will become operative to arrest the downward movement of platform 34 in the manner described previously.

It will be recalled that when platform 34 is in midspan, collector current flows from transistor T3 to hold the base of transistor T4 positive relative to its emitter so that no T4 collector current flows through relay 86. When the platform 34 is rising, however, so that the rack 64 is moving from its dotted position toward its full position in FIG. 2, the wiper 67 is moving clockwise from its dotted toward its full position thereby increasing the potential difference between the positive terminal '73 and the wiper terminal 70 and causing an increased current to flow in resistors R1 and R2. When the platform 34 reaches its upper reference point, determined by the position of tap 87, the current through resistor R2 will have increased to the point where the base of transistor T3 has become sufliciently positive relative to its emitter to cause T3 to become non-conductive. This turns transistor T4 on, energizing relay 86, which will arrest such upward movement in the manner described hereinabove.

Refer now to FIG. 3, which shows the relay circuitry for setting the potentiometer wipers 87 and 87. The various components of the relay circuitry of FIG. 3 is connected to be energized from power supply conductors 128 and 129 which are connected to any suitable source of energy.

Before initiating the operation of the circuitry of FIG 3, the platform 34 is first lowered to the desired lower set point relative to the ladle 11, i.e., its'dotted'position in FIG- 1, by closing the by-pass contact 136 to energize the solenoid 55. When this lower desired reference point is reached contact 36 is released. The wiper terminal 67 will also be in its dotted position so that the potential on terminal 70 will be at the lower limit value. However, wiper 87 will be held in a central position on potentiometer P1 by spring 156 so that the resistance between the emitter and base of transistor T1 will not be suflicient to maintain said transistor in a non-conductive, reverse biased condition so that relay 85 will be energized. As a result, normally open contacts 858, which are in circuit with the motor 120 between supply conductors 128 and 129, will be closed.

In order to initiate the setting of the lower reference point, the lower limit set push button 140 is closed to complete an energizing circuit through the clutch solenoid 123 which engages the clutch 122. In addition, holding relay 142, connected in parallel with the clutch 123 by conductor 144, is also energized to close contacts 142A thereby maintaining the energizing circuit to the clutch 123 through conductor 145. In addition, contacts 142B also close to complete an energizing circuit to the motor 120 through contacts 85B, 142B and the normally closed contacts 147A of relay 147.

The motor 120 now begins driving the potentiometer wiper 87 through the clutch 122. As potentiometer wiper 87 moves, the resistance between the emitter and base of transistor T1 increases. When the potentiometer wiper 87 reaches a position corresponding to the position of platform 37, the potential difference between the emitter and base of transistor T1 will be sufficiently high to reverse bias said transistor. As a result, relay 85 drops out to open contacts 85B which de-energizes the motor 120 so that the potentiometer Wiper 87 comes to rest. In addition, normally closed contacts 85C will close to complete an energizing circuit to a relay 150 which in turn closes contacts 150A to energize a relay 152. Upon this event contacts 152A close to complete the energizing circuit to a relay 147 which opens contacts 147A to prevent further energization of the motor and to lock it in its present position. The potentiometer wiper 87 is now in its lower reference point position.

After the lower limit reference point has been established, the by-pass switch 137, see FIG. 1, is closed to energize the solenoid 47 so that the platform 34 and vessel begin moving upwardly. When the desired upper limit of the vessel 10 is achieved, that is, that point at which the lower end of the nozzle 20 will remain immersed in the molten metal 12, the by-pass contacts 137 will be released to de-energize the solenoid 47 and close the valve 46 so that upward movement of the vessel 10 stops.

Because the potentiometer wiper 87' is initially held in a central position by spring 156' before its reference point is established, the potential difference between the emitter and base of transistor T3 will be sufficiently large to hold the base of transistor T3 positive with respect to its emitter so that T3 will be non-conductive. As a result, the base of T4 will be negative relative to its emitter so that collector current will flow to energize relay 86.

With relay 86 energized, contacts 86B in the energizing circuit of motor 120 will be closed. Thus, when the upper limit reference point contacts 140 are closed, clutch solenoid 123' and holding relay 142' will be energized to engage the clutch 122' and to close the by-pass contacts 142'A around the upper limit push button 140' and the contacts 142B in the motor 120' energizing circuit so that said motor begins driving the wiper 87'.

When the wiper 87' of potentiometer P2 reaches a position corresponding to the position of the vessel 10, the potential between the emitter and base of transistor T3 will no longer be sufiicient to hold said transistor in a reversed biased direction and T3 will begin conducting. As a result, T4 will become non-conductive and relay 86 de-energized. Contacts 86B will then open to de-energize the motor so that movement of the potentiometer wiper 87' will be stopped and contacts 86C will close to energize relay Upon the latter event, contacts 150A will close to energize relay 152 which, in turn, closes contacts 152A to energize lockout relay 147'. With relay 147' energized, contacts 147 open and thereby lock the motor 120 in its reference point position.

It can be seen that during cyclic operation of the vessel 10, the positions of wipers 87 and 87' will be set. As a result, downward movement will be arrested when the potential of the vessel 10 on wiper terminal 70, as reflected by the current through R1, corresponds to the position of wiper 87. Similarly upward movement will be stopped when the position of wiper 67, as reflected by the current through R2, corresponds to the position of wiper 87'. On the other hand, when the reference points of wipers 87 and 87' are to be set, the wiper 67 is first placed in one position and then the wiper terminal 87 is driven until its position corresponds to one of the positions of wiper 67 and then movement of the wiper 87 is arrested in its reference point position. The reference point of wiper 87' is established in a similar manner.

The potentiometer wipers 87 and 87 will remain in their upper and lower reference point positions until released by operation of the lower limit return push button 154 which is in the energizing circuit of the lower limit clutch solenoid 123 or the upper limit return button 154' which is in the energizing circuit of the upper limit clutch solenoid 123. Opening of either of the push buttons 154 or 154 will de-energize the clutch solenoids 123 and 123 allowing the potentiometer wipers 87 and 87 to be returned to their initial neutral position by operation of springs 156 and 156', see FIG. 2. In addition, operation of the push buttons 154 and 154' will deenergize the holding relays 142 and 142 so that the relay circuit of FIG. 3 will be returned to its initial condition with the relays 142, 142, 147, 147, 150, 150', 1 52 and 152', all de-energized.

While the invention has been shown and described in relation to degassing apparatus where the platform 34 is movable and the ladle 11 inert, it will be understood by those skilled in the art that the invention has application as well to an arrangement wherein the vessel 10 is stationary and the ladle 11 vertically movable. In the latter instance, the tracking rack 64 would be affixed to the movable ladle.

I claim:

1. Apparatus for degassing molten metal including, a vacuum vessel, a container for said molten metal disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, reversible driving means for producing relative movement between said vessel and said container toward and away from each other so that molten metal may be cyclically drawn into and discharged from said vessel, a tracking potentiometer means coupled to said driving means for producing a voltage signal proportional to the distance between said vessel and container, control means in circuit with said potentiometer means and including first and second reference potentiometer means and voltage responsive means operative to render said driving .means inefiective to continue relative movement of said vessel and container away from each other when said tracking potentiometer signal has a predetermined relation to said first reference potentiometer signal, said voltage responsive means also being operative to render said driving means ineffective to continue relative movement of said vessel and container toward each other when said tracking potentiometer signal has a predetermined relation to said second reference potentiometer signal.

2. In apparatus for degassing molten metal including a vacuum vessel and a container for said molten metal disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, reversible driving means for producing relative movement between said vessel and said container toward and away from each other so that said passageway may be immersed to varying depths beneath the surface of the metal within said container, tracking means coupled to said driving means for producing an electrical tracking signal proportional to the distance between said vessel and said container, control means in circuit with said tracking means, said control means having first and second adjustable reference means for producing a first and second electrical reference signal, said control means including signal comparison means and first and second normally inactive output means, said signal comparison means being operative to actuate said first output means to render said driving means ineffective to continue relative movement of said vessel and container away from each other when said tracking signal and said first reference signal have a predetermined relation and operative to actuate said second output means to render said driving means ineffective to continue relative movement of said vessel and container toward each other when said tracking signal and said second signal have a predetermined relation.

3. Apparatus for degassing molten metal including, a vacuum vessel, a container for said molten metal, disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, driving means for producing relative movement between said vessel and said container toward and away from each other so that said passageway may be immersed to varying depths beneath the surface of the metal within said container, adjustable tracking impedance means coupled to said driving means for producing an electrical sign-a1 proportional to the distance between said vessel and said container, control means in circuit with said tracking impedance means, said control means having first and second adjustable reference impedance means for producing first and second electrical reference signals, said control means including signal comparison means operative to render said driving mean ineffective to continue relative movement of said vessel and container away from each other when said tracking signal and first reference signal have a predetermined relation and operative to render said driving means ineffective to continue relative movement of said vessel and container toward each other when said tracking signal and said second reference signal have a predetermined relation.

4. Apparatus for degassing molten metal including, a vacuum vessel, a container for said molten metal disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, driving means for producing relative movement between said vessel and said container toward and away from each other so that said passageway may be immersed to varying depths beneath the surface of the metal within said container, tracking potentiometer means coupled to said driving means for producing a tracking voltage signal proportional to the distance between said vessel and said container, control means in circuit with said tracking potentiometer means, said control means having a first and second reference potentiometer means for producing first and second reference voltage signals, said control means including electronic means in circuit to receive said tracking signal and said first reference signal and operative to produce a first output signal when said tracking signal and said first reference signal have a predetermined relation, first output means in circuit with said first electronic means and responsive to said first output signal for rendering said driving means ineffective to continue relative movement of said vessel and container away from each other, second electronic means in circuit to receive said tracking signal and said second reference signal and operative to produce a second output signal when said tracking signal and said second reference signal have a predetermined relation, and second output means in circuit with said second'electronic mean and responsive to said second output signal for rendering said driving means ineffective to continue relative movement of said vessel and container away from each other.

5. Apparatus for degassing molten met-a1 including, a vacuum vessel, a container for said molten metal disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, reversible driving means for producing relative movement between said vessel and said container so that molten metal may be cyclically drawn into and discharged from said vessel, tracking means coupled to said driving means for sensing the relative positions of said vessel and container and for producing an electrical tracking signal proportional thereto, control means in circuit with said tracking means and having first and second adjustable reference means for producing first and second electrical reference signals, first and second selectively operable motive means for adjusting said first and second adjustable means respectively, said control means also including signal comparison means for rendering said driving means ineffective to continue relative movement of said vessel and container away from each other and for rendering said first motive means inactive to adjust said first reference means when said tracking signal and first reference signal have a predetermined relation, said signal comparison means also being operative to render said driving mean ineffective to continue relative movement of said vessel and ladle toward each other and to render said second motive means inactive to adjust said second reference means when said tracking signal and said second reference signal have a predetermined relation.

6. In apparatus for degassing molten metal, the combination of, a vacuum vessel, a container for said molten metal disposed below said vessel, a molten metal interconnecting assageway extending from said vessel and to- Ward said container so that said molten metal may be conducted to the interior of said vessel from said container, reversible driving means for producing relative movement between said vessel and said container so that molten metal may be cyclically drawn into and discharged from said vessel, tracking means coupled to said driving means for sensing the relative positions of said vessel and container and for producing an electrical tracking signal proportional thereto, control means in circuit with said tracking means for producing first and second adjustable reference signals, motive means for selectively adjusting said first and second reference signals, said control means being operative to render said driving means ineffective to continue relative movement of said vessel and container in one direction and to render said motive means ineffective to adjust said first reference signal when said first tracking signal and said first reference signal have a predetermined relation, said last control means also being operative to render said driving means ineffective to continue relative movement of said vessel and ladle in an opposite direction and to render said motive means ineffective to adjust said second reference signal when said tracking signal and said second signal have a predetermined relation.

7. Apparatus for degassing molten metal'incl'uding, a vacuum "vessel, a container for said molten metal disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, reversible driving means for producing relative movement between said vessel and said container so that molten metal may be cyclically drawn into and discharged from said vessel, adjustable tracking resistance means coupled to said driving means for producing an electrical signal proportional to the distance between said vessel and said container, control means in circuit with said tracking resistance means, said control means having a first adjustable reference resistance means for producing a first reference signal and a second adjustable resistance means connected to a constant voltage source for producing a second reference signal, first and second selectively operable motive means for adjusting said first and second adjustable resistance means respectively, said control means including signal comparison means and output means for comparing said electrical signals and for rendering said driving means ineffective to continue relative movement of said vessel and container away from each other and for rendering said first motive means inactive to adjust said first reference means when said electrical signal and said first reference signal have a predetermined relation, said signal comparison and output means also being operative to render said driving means ineffective to continue relative movement of said vessel and container toward each other and to render said second motive means inactive to adjust said second reference means when said electrical signal and said second reference signal have a predetermined relation.

8. Apparatus for degassing molten metal including, a vacuum vessel, a container for said molten metal disposed below said vessel, a molten metal interconnecting passageway extending from said vessel and toward said container so that said molten metal may be conducted to the interior of said vessel from said container, reversible driving means for producing relative movement between said vessel and said container so that molten metal may be cyclically drawn into and discharged from said vessel, a tracking potentiometer coupled to said driving means for producing a tracking voltage signal proportional to the distance between said vessel and said container, control means for establishing the limits of relative movement between said vessel and said container toward and away from each other, said control means having first and second reference potentiometer means producing first and second reference voltage signals respectively, a means for actuating said driving means independently of said control means, first and second motive means for adjusting said first and second reference potentiometer means respectively, said control means including a first electronic means in circuit with said tracking potentiometer and said first reference potentiometer for producing an output signal when said first electrical signal and said upper limit signal have a predetermined relation, and a first output means for rendering said driving means ineffective to continue relative movement of said vessel and container away from each other and for rendering said first motive means inactive to adjust said first reference potentiometer means, said control means also including second electronic means in circuit with said tracking potentiometer and said second reference potentiometer for producing an output signal when said first electrical signal and said lower limit signal have a predetermined relation, and second output means for rendering said driving means ineffective to continue relative movement of said vessel and ladle toward each other and to render said second motive means inactive to adjust said second adjustable means.

9. Apparatus for degassing molten metal including, a vacuum vessel and a molten metal container disposed below said vessel, an inlet passage extending from said vessel and toward said container, driving means for producing relative movement between said vessel and container so that said passage may be immersed to varying depths beneath the surface of the metal within said container and said metal cyclically conducted between said vessel and container, tracking potentiometer means coupled to said driving means for producing a tracking voltage signal proportional to the distance between said vessel and said container, control means in circuit with said tracking potentiometer means and including a first and second reference potentiometer means for producing first and second reference voltage signals, said control means also including first and second electronic circuit devices each having a control element and a pair of output elements and each being conductive when the control element voltage signal has a predetermined relation to the voltage on one output element, the control elements and one of the output elements of said first electronic circuit device being connected to receive said tracking voltage signal and one of said reference voltage signals so that said first electronic circuit device will change its conductive state when said tracking voltage signal and said first reference voltage signal have a predetermined relation, first output means in circuit with said first electronic circuit device and responsive to a change in the conductive state thereof for rendering said driving means ineffective to continue relative movement of said vessel and said container away from each other, the control element and one of the output elements of said second electronic circuit device being connected to receive said tracking signal and the other of said reference signal so that said second electronic circuit device will change its conductive state when said tracking voltage signal and said second reference voltage signal have a predetermined relation, second output means in circuit with the other output element of said second electronic circuit device and responsive to change in the conductive state thereof for rendering said driving means ineffective to continue relative movement of said vessel and said container toward each other.

10. Apparatus for degassing molten metal including, a vacuum vessel and a molten metal container disposed below said vessel, an inlet passage extending from said vessel and toward said container, driving means for producing relative movement between said vessel and container so that said passageway may be immersed to varying depths beneath the surface of the metal within said container and said molten metal cyclically conducted between said vessel and container, tracking potentiometer means coupled to said driving means for producing a tracking voltage signal proportional to the distance between said vessel and said container, control means in circuit with said tracking potentiometer means and including first and second reference potentiometer means for producing first and second reference voltage signals and firs-t and second transistors, the base-emitter circuit of said first transistor being connected to receive a tracking voltage signal and said first reference voltage signal so that said first transistor will change its conductive state when said tracking voltage signal has a predetermined relation to said first reference voltage signal, first output relay means connected to the emitter of said first transistor and operative when the conductive state of said first transistor changes to render said driving means ineffective to continue relative movement of said vessel and said container away from each other, the base-emitter circuit of said second transistor being connected to receive said tracking voltage signal and said sec-ond reference voltage signal whereby said second transistor will change its conductive state when said tracking voltage signal has a predetermined relation to said second reference voltage signal, and second output relay means connected to the collector of said second transistor and operative upon a change in theconductive state thereof to render said driving means ineffective to continue relative movement of said vessel and container toward each other.

11. Apparatus for degassing molten metal including, a vacuum vessel and a molten metalcontainer dispose-d below said vessel, an inlet passage extending from said vessel and toward said container, reversible driving means for producing relative movement between said vessel and container so that molten metal may be cyclically drawn into and discharged from said vessel, tracking means coupled to said driving means for sensing the relative positions of said vessel and said container and for producing an electrical signal proportional thereto, control means in circuit with said tracking means and including means for establishing first and second electrical reference signals corresponding to the desired limits of relative movement between said vessel and said container, adjusting means for independently changing said first and second reference signals, means for independently actuating said reversible driving means, said control means being operative to render said driving means ineffective in one direction and also being operative to render said adjusting means ineffective to change said first reference signal when said electrical signal has a predetermined relation to said first reference signal, said control means being additionally operative to render said driving ineffective in an opposite direction and to render said adjusting means ineffective to change said second reference signal when said electrical signal has a predetermined relation to said second reference signal.

12. Apparatus for degassing molten metal including, a vacuum vessel and a molten metal container disposed below said vessel, an inlet passage extending from said vessel and toward said container, reversible driving means for producing relative movement between said vessel and said container so that molten metal may be cyclically drawn into and discharged from said vessel, potentiometer means coupled to said driving means for producing a voltage signal proportional to the distance between said vessel and container, control means including first and second adjustable resistance means for producing first and reference voltage signals, adjusting means for independently changing said first and second resistance means, said control means being in circuit with said potentiometer means and being operative when said potentiometer voltage signal has a predetermined relation to said first reference voltage signal to render said driving means ineffective to continue relative movement of said vessel and container away from each other and to render said adjusting means ineffective to adjust said first resistance means, said control means being operative to render said driving means ineffective to continue relative movement of said vessel and container toward each other and to render said adjusting means ineffective to adjust said second resistance means when said potentiometer voltage signal has a predetermined relation to said second reference voltage signal.

13. Apparatus for degassing molten metal including, a vacuum vessel and a molten metal container disposed below said vessel, an inlet passage extending from said vessel and toward said container, driving means for producing relative movement between said vessel and said container so that said passage may be immersed to varying depths beneath the surface of the metal within said container and said metal cyclically conducted between said vessel and container, tracking potentiometer means coupled to said driving means for producing a tracking voltage signal proportional to the distance between said vessel and said container, control means in circuit with said tracking potentiometer means and including a first and a second reference potentiometer means for producing first and second reference voltage signals, first and second adjusting means for independently adjusting said first and second potentiometer means to change said reference voltage signals, said control means also including first and second electronic circuit devices each having a control element and a pair of output elements and each being conductive when its control element voltage signal has a predetermined relation to the voltage on one of its output elements, the control element and one of the output elements of said first electronic circuit device being connected to receive said tracking voltage signal and one of said reference voltage signals so that said first electronic circuit device will change its conductive state when said tracking voltage signal and said first reference voltage signal have a predetermined relation, first output means in circuit with said first electronic circuit device and responsive to a change in the conductive state thereof for rendering said driving means ineffective to continue relative movement of said vessel and said container away from each other and for rendering said first adjusting means ineffective to adjust said first potentiometer means, the control element and one of the output elements of said second electronic circuit device being connected to receive said tracking signal and the other of said reference signals so that said second electronic circuit device will change its conductive state when said tracking voltage signal and said second reference voltage signal have a predetermined relation, second output means in circuit with the other output element of said second electronic circuit device and responsive to change in the conductive state thereof for rendering said driving means ineffective to continue relative movement of said vessel and said container toward each other and for rendering said first adjusting means ineffective to adjust said second potentiometer means.

14. Apparatus for degassing molten metal including, a vacuum vessel and a molten metal container disposed below said vessel, an inlet extending from said vessel and toward said container, driving means for producing relative movement between said vessel and container so that said passageway may be immersed to. varying depths beneath the surface of the metal within said container and said molten metal cyclically con-ducted between said vessel and container, tracking potentiometer means coupled to said driving means for producing a tracking voltage signal proportional to the distance between said vessel and said container, control means in circuit with said tracking potentiometer means and including first and second reference potentiometer means for producing first and second reference voltage signals and first and second transistors, the base-emitter circuit of said first transistor being connected to receive said tracking voltage signal and said first reference voltage signal so that said first transistor will change its conductive state when said tracking voltage signal has a predetermined relation to said first reference voltage signal, first and second e'lectromotive means for respectively adjusting said first and second potentiometer means, first output relay means connected to the emitter of said first transistor and operative when the conductive state of said first transistor changes to render said driving means ineffective to continue relative movement of said vessel and said container away from each other and to open circuit said first electr-omotive means, the base-emitter circuit of said second transistor being connected to receive said tracking voltage signal and said second reference voltage signal whereby said second transistor will change its conductive state when said tracking voltage proportional signal has a predetermined relation to said second reference voltage signal, and second output relay means connected to the collector of said second transistor and operative upon a change in the conductive state thereof to render said driving means ineffective to continue relative movement of said vessel and container toward each other and to open circuit said second electromotive means.

References Cited by the Examiner UNITED STATES PATENTS 8/1953 Jacques 121-41 7/1958 Sager et a1 2220 

1. APPARATUS FOR DEGASSING MOLTEN METAL INCLUDING, A VACUUM VESSEL, A CONTAINER FOR SAID MOLTEN METAL DISPOSED BELOW SAID VESSEL, A MOLTEN METAL INTERCONNECTING PASSAGEWAY EXTENDING FROM SAID VESSEL AND TOWARD SAID CONTAINER SO THAT SAID MOLTEN METAL MAY BE CONDUCTED TO THE INTERIOR OF SAID VESSEL FROM SAID CONTAINER, REVERSIBLE DRIVING MEANS FOR PRODUCING RELATIVE MOVEMENT BETWEEN SAID VESSEL AND SAID CONTAINER TOWARD AND AWAY FROM EACH OTHER SO THAT MOLTEN METAL MAY BE CYCLICALLY DRAWN INTO AND DISCHARGED FROM SAID VESSEL, A TRACKING POTENTIOMETER MEANS COUPLED TO SAID DRIVING MEANS FOR PRODUCING A VOLTAGE SIGNAL PROPORTIONAL TO THE DISTANCE BETWEEN SAID VESSEL AND CONTAINER, CONTROL MEANS IN CIRCUIT WITH SAID POTENTIOMETER MEANS AND INCLUDING FIRST AND SECOND REFERENCE POTENTIOMETER MEANS AND VOLTAGE RESPONSIVE MEANS OPERATIVE TOO RENDER SAID DRIVING MEANS INEFFECTIVE TO CONTINUE RELATIVE MOVEMENT OF SAID VESSEL AND CONTAINER AWAY FROM EACH OTHER WHEN SAID TRACKING POTENTIOMETER SIGNAL HAS A PREDETERMINED RELATION TO SAID FIRST REFERENCE POTENTIOMETER SIGNAL, SAID VOLTAGE RESPONSIVE MEANS ALSO BEING OPERATIVE TO RENDER SAID DRIVING MEANS INEFFECTIVE TO CONTINUE RELATIVE MOVEMENT OF SAID VESSEL AND CONTAINER TOWARD EACH OTHER WHEN SAID TRACKING POTENTIOMETER SIGNAL HAS A PREDETERMINED RELATION TO SAID SECOND REFERENCE POTENTIOMETER SIGNAL. 